Synthesis gas generation apparatus

ABSTRACT

Apparatus for generating high pressure synthesis gas containing hydrogen and carbon oxides and useful in Oxo processes, hydrogen production, and in the production of ammonia, methanol and the like. The apparatus includes a furnace, a novel arrangement of a combustion turbine exhausting into the furnace to supply preheated oxygen thereto and a sequence of heaters and reactors for alternately heating the reaction mixture in the furnace and adiabatically reacting the mixture outside the furnace to enable reaction and thus gas product at higher pressures than previously obtained. The mentioned heater-reactor sequence minimizes waste heat in the furnace and makes its recovery, e.g. as steam, no longer of such major economic importance to the process, enabling use of a combustion turbine both to supply preheated oxygen to the furnace and to drive plant machinery such as compressors for air to be fed to the secondary reformer in ammonia synthesis gas production.

United States Patent Bogart Mar. 5, 1974 SYNTHESIS GAS GENERATIONAPPARATUS [75] Inventor: Marcel J. P. Bogart, Whittier, Calif.

[73] Assignee: Fluor Corporation, Los Angeles,

Calif.

[22] Filed: June 28, 1971 21 Appl. No.: 157,452

[52] US. Cl 23/262, 423/656, 23/288 K, 23/289, 260/4495, 252/373, 48/197[51] Int. Cl BOlj 9/04 [58] Field of Search.. 23/260, 212 A, 212 R, 288K,

[56] References Cited UNITED STATES PATENTS 2,443,773 6/1948 Matuszak23/288 K 3,012,962 12/1961 Dygert 23/260 X 3,446,747 5/1969 Bongiorno23/212 A X Primary Examiner.lames l-l. Tayman,- 1r. Attorney, Agent, orFirm-Louis J. Bachand [57] ABSTRAGI Apparatus for generating highpressure synthesis gas containing hydrogen and carbon oxides and usefulin Oxo processes, hydrogen production, and in the production of ammonia,methanol and the like. The apparatus includes a furnace, a novelarrangement of a combustion turbine exhausting into the furnace tosupply preheated oxygen thereto and a sequence of heaters and reactorsforalternately heating the reaction mixture in the furnace andadiabatically reacting the mixture outside the furnace to enablereaction and thu s gas product at higher pressures than previouslyobtained. The mentioned heater-reactor sequence minimizes waste heat inthe furnace and makes its recovery, e.g. as steam, no longer of suchmajor economic importance to the process, enabling use of a combustionturbine both to supply preheated oxygen to the furnace and to driveplant machinery such as compressors for air to be fed to the secondaryrefa 700 700 "F 1 SYNTHESIS GAS GENERATION APPARATUS BACKGROUND OF THEINVENTION This invention has to do with apparatus for synthesis gasgeneration and, more particularly, is concerned with apparatus enablingthe obtainment of synthesis gas at higher pressures than heretofore,with increased heat utilization efficiencies and at lower overall cost.

Synthesis gas is a term applied to raw material gas streams containinghydrogen and carbon oxides which may be converted, synthesized, intoproducts for which there is considerable commercial demand, e.g.methanol, hydrogen, ammonia and x0 process products. A basic route tosuitable synthesis gases is the steam reforming of hydrocarbon vaporswhich form a readily available and low cost source of hydrogen andcarbon. In steam reforming, a reactionmixture of steam and hydrocarbonvapor, ranging from methane to naphtha and higher molecular weighthydrocarbons, is contacted at high temperatures, 1000F and above, and atelevated pressures with a suitable catalyst. The catalytic reaction withthe steam converts the hydrocarbon raw material into hydrogen and carbonoxides. The basic reactions taking place include:

1. Cl-I, B 0 55) C0 3 H for methane, and

2. C I-I 6 H O 6 C0 13 H for hexane, and

similarly for other hydrocarbon vapors. The CO and H 0 may react to formCO and additional l-I by the so-called water-gas shift reaction Anexcess of steam (H O), over the stoichiometric amount indicated in theequations (1) and (2) above, is typically employed to force theequilibrium in the reforming reactions toward the right hand side ofequations (1) and (2). Such stoichiometric excess of steam will alsomaximize conversion of carbon monoxide by the shift reaction, equation(3). Should a deficiency in CO thus develop, e.g. for a synthesis gas tobe used in methanol production according to the equation 4. CO+2H CH OHthere may be added CO to the reaction mixture for the generation in thereforming process of CO, as by overall equation 5. CO 3 CH +2 H O 4 (C02H In producing the above-mentioned commercially important products andothers, the generated synthesis gas leaving the steam reforming processis subjected to further treatments, e.g. equation (4) above. Suchtreatments frequently desirably or necessarily involve the use of quitehigh pressure, e.g. 500 psig and even considerably higher pressures inthe range of 1500 psig to 10,000 psig.

Raw synthesis gas obtained from the reformer at lower pressures thusmust be compressed to desirable further treatment pressuresnecessitating high energy costs and capital expense for the compression.PRIOR ART.

To my knowledge, synthesis gases containing hydrogen and carbon oxidesat higher pressures than 400-500 psig are not economically obtainable inheretofore known steam reformers. The limitation on pressures obtainableis inherent in the design of presently known catalytic reformingreactors, given the present state of construction material development.

In presently used steam reforming apparatus, a plurality of catalystfilled tubes,- vertically disposed within a furnace, are used as thereaction zone. The tubes are located specifically inside the firebox orradiant heating section of the furnace and are there subjected toradiant heat from a surrounding multiplicity of burners burning asuitable fuel and arranged to give a high uni.- forrnity of heatdistribution. The catalyst containing tubes necessarily are formed ofhigh heat resistant alloy material. These tubes may be 20 to 40 feet inlength, have inside diameters of 3 to 5 inches, and a wall thickness of0.5 to 0.75 inch and more. The tubes are filled throughout their lengthwith reforming catalyst of well known and conventional composition,typically in the form of hollow cylinders 0.37 inch in the outsidediameter and 0.37 inch in length. Being located in the radiant heatingsection of the furnace, these catalyst containing tubes are heated to asubstantial temperature by the burner flames. For example, in generationof an ammonia synthesis gas, a steam-hydrocarbon vapor mixture preheatedto e.g. 900F enters the catalyst tubes and must be heated to over 1400Fin the course of passage through the tubes requiring the furnacecombustion gases to reach temperatures of 1900F and more.

The catalyst containing tubes are subject to maximum heat stress attheir outer wall near the bottom of the firebox. Temperatures on theouter tube skin will likely be F to 200F higher than the exittemperature of the treated reaction mixture, e.g. 1600F and higher. Suchtemperatures are in the critical region for the tube metal, where theallowable design stress of the alloys available drops off sharply. Forexample, a 304 stainless alloy undergoes a loss of strength from 2,500psi at l600F to 1,200 psi at 1800F and to only 500 psi at 2000F.

The suitable wall thickness of a catalyst containing tube for a reformeris given by the formula wherein P is the operating pressure, D, the tubediameter, S, the allowable stress and f, a design safety factor. Theeconomical upper limit of wall thickness for reformer tubes is about oneinch. The typical tube dimensions and maximum heated gas temperaturementioned above combine to limit the allowable internal gas pressurewithin these tubes to about 500 psig for presently commercially employedand foreseeable alloys.

Modifications of tube design such as reduction of diameter D could raisethe allowable pressure limit without an increase in wall thickness, 2.Because the tube is used to contain a catalyst bed, fluid flow and heatand mass transfer characteristics are significant and a reduced tubediameter would necessitate a correspond-- ing decrease in catalystparticle size. The use of smaller catalyst pellets would, however,require a reduction in reaction mixture velocity through the tubes tokeep the gas pressure drop through the tube at an acceptably low level.This change would require a markedly increased number of tubularelements at greatly increased cost for the radiant section of thereformer.

Moreover, the increase in gas volume as reactions (1) and (2) proceedrequires raising of the final temperature as the operating pressure goesup to maintain levels of unconverted hydrocarbon, methane leak,reasonably constant and near the thermodynamic equi librium value.According to the above tube wall thickness formula, the tube wallthickness could be cumulatively increased by the dual effect of theraised pressure and the further dropping of the already low value ofallowable stress by the increase in operating temperature.

A further significant aspect of present reforming ap paratus is unduewaste in heat utilization. Reformer furnaces are highly specialized,expensive apparatus for supplying heat for the reforming reaction.l-Ieat for the reforming reaction includes that necessary to preheatfeed and to raise process steam as well as heat supplied to thereactants as the reforming reactions proceed. It is obviouslyundesirable to use the reformer to supply heat other than that requiredfor reforming, since such auxiliary heat can generally be supplied moreeconomically by other means. As noted above, in previously knownreformers, the burner tubes are located in the firebox or radiantheating section of the furnace. Combustion gases used to heat thereactor tubes leave the radiant section of the furnace at temperaturesabove 1900F, i.e. with tremendous heat contents most of which are notuseable to further the reforming reaction. Cooling these flue gases tosay 500F or less for the sake of economic heat utilization beforeventing them to the atmosphere will provide a quantity of sur plus heatapproximately as great as all the heat used to effect the reformingreaction. Thus the minimum fired duty for a known reformer furnace isnearly approximately double that duty required to satisfy the reformingreaction. Economy of operation dictates that a use must be foundelsewhere in the process or plant for about one-half of the fired dutyof the conventional reformer furnace; such uses include preheating airfor the secondary reformer, if used and generation and superheating ofprocess and motive steam. Obviously, an ap paratus enabling a closertailoring of furnace fired duty to reforming reaction requirements couldmean significant fuel savings over conventional apparatus.

SUMMARY OF THE INVENTION It is a major objective of the presentinvention to provide apparatus for obtaining high pressure synthesis gasfrom a conventional reformer reaction mixture by satisfying, the highendothermic heat requirements in a novel manner including feedingpreheated oxygen to the furnace from a combustion turbine, using theturbine mechanical energy output as needed in the plant or elsewhere,and freeing the catalyst containing vessel from exposure to fireboxlevel temperatures while retaining high reaction mixture temperaturesneeded for efficient conversion of the reaction mixture into synthesisgas.

It is a further objective of the invention to have the fired duty of thefurnace more closely approximate reforming reaction heat requirements,whereby substantial fuel savings are realized.

Specifically there may be mentioned these advan tages of the presentinvention process:

The generated synthesis gas is delivered at high pressures loweringcompression requirements for fur ther treatment operations;

The catalyst containingvessels are widely variable in design and inmaterials of fabrication;

The radiant heating and convection heating sections of the furnace areeach used to advantage because the endothermic heat of reforming doesnot have to be transferred entirely within the radiant section of thefurnace;

' 4 The catalyst beds may be tailored both chemically and physically,for maximum effect in particular 'reactions, in sequence, as thereaction mixture composition changes, or for specific effects; Catalystlife may be improved by specific adaptation and its cost loweredinitially and during operation;

Capital costs are reduced by the elimination of dual demands forsimultaneously high pressure and very high temperature resistance in thereaction vessel.

Other objects will become apparent hereinafter.

The foregoing and other objects are realized with apparatus according tothe invention for generating a synthesis gas including plural adiabaticreactors in series flow connection for progressively catalyticallyreforming a preheated mixture of steam and hydrocarbon vapor intohydrogen and carbon oxides, plural heaters sequenced with these reactorseach to heat the mixture for adiabatic reforming in its succeedingreactor, a furnace supplying heat to the heaters, and combustion turbinemeans having a mechanical energy output, the turbine means beingarranged to exhaust oxygen containing combustion gases into the furnaceto supply preheated oxygen to the furnace either as the sole source ofoxygen to the furnace or with supplemental air to the furnace. Specificfeatures of the apparatus include in certain embodiments, meanssupplying fuel to the furnace for combustion with the preheated oxygenin a manner to generate, e.g. only about 1 10 percent (without use ofsecondary reformer) and in general not more than 125 percent of the heatrequired for the reforming reactions, means utilizing the mechanicalenergy output of the turbine means, a secondary reactor and means forsupplying compressed gases such as air from an air supply means to thesecondary reactor, optionally with preheating in air heating meanswithin the furnace, including compressor means such as a centrifugalcompressor driven by'the mechanical energy output of the combustionturbine means.

In preferred embodiments, the apparatus furnace is longitudinallyextended and has a firebox at one end. The plural heating means aredistributed in spaced relation along at least a portion of the furnaceinterior length, at least one of the heating means being located withinthe firebox portion of the furnace. The plural reactors may then belocated outside the furnace whereby the reaction mixture passesalternately into the heaters within the furnace and into reactorsoutside the furnace. The furnace interior may be downwardly temperaturegraded out from the firebox and successive heating means disposedprogressively closer to the firebox whereby reaction mixturetemperatures increase in successive reactors sequenced with the heat ingmeans.

The apparatus plural reactors may comprise an initial primary reactor,at least one intermediate primary reactor and a final primary reactor.The heating means in advance of the initial reactor may be arrangedwithin the furnace to heat the initial reactor feed to a temperatureabove about 750F, the heating means in advance of the intermediatereactor may be arranged within the furnace to heat the intermediatereactor feed to a temperature above about 900F, and the heating means inadvance of the final reactor may be arranged within the furnace to heatthe final reactor feed to a temperature above about i 4-O0F. Theapparatus may further include means maintaining the pressure within thereactors above about 700 psig.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS In the present apparatus the heating and reacting stagesessential to generation of synthesis gas containing carbon oxides andhydrogen from steam and hydrocarbon vapor are separated and the catalystcontaining reactor vessels removed from the heating zone. so that thehigh temperatures there present are not visited unduly upon the reactorvessels. The reaction is conducted adiabatically, i.e. without theinputof heat into the reactor other than by preheating the feed to thereactor. .This accordingly reduces substantially heat stresses in thereactor vessels, and thus enables wide variability in their design andmost importantly frees the synthesis gas generation operation fromartificial constraints on pressures usable, to enable obtaining ofhigher pressure synthesis gas. The preheating of the reactor feed gasesmay be done in small-diameter thinwall tubes, reducing their outer skintemperature and allowing their operation at higher internal pressures.

vWith reference to the drawing an alternating arrangement of adiabaticreactors and heating coils is shown for carrying out the presentinvention. Furnace l is a longitudinally extended structure of suitableheat resistant material having a higher temperature, radiant heatingfirebox section 2 and a lower temperature, convection heating section 3.The furnace may be horizontally disposed as well. Burners 4 are locatedin lower furnace firebox section 2 for burning the combustible mixtureintroduced throughvlines 5a, 6 and sometimes 6a to the furnaceburners.Primary oxygen to the firebox is provided along line 5a from expander 5of the combustion turbine. Turbine exhaust generally containing about 17percent oxygen by volume is fed along line 5a to burners 4 in thefirebox 2. Supplementary oxygen may be fed to the burners 4 in firebox 2from line 6a carrying supplementary air to the burners. Flue gases andother products of combustion and their associated heat contents travelupwardly through the furnace l to the convection section 3 so that thefurnace interior'7 is at progressively lower heated condition upwardalong its length. The furnace ll terminates in a conventional stack at8.

A mixture of steam and hydrocarbon feed vapors is fed to the furnace forheating to desired temperatures and catalytic reaction in contact withcatalytically effective amount of a suitable catalyst known per se forconversion of the steam and hydrocarbon vapor into carbon oxides andhydrogen.

The steam portion of the feed comprises superheated steam which may beobtained using the furnace heat or from some nearby process or othersource. l-Iigh pressure steam is passed along line 12 for preheating incoil 12a before being combined with hydrocarbon vapors entering thesystem through line 13, the steam from coil 12a being at suitabletemperature and pressure for initiating the reforming reaction afterbeing mixed with hydrocarbon vapors from: line l3.

Thus, the hydrocarbon vapors in line l3 comprising methane, ethane,propane, butanes, pentanes, hexanes and the like up to naphthas orhigher hydrocarbons, or any of these, and at a temperature of about 750Fand a pressure of 800 psig are mixed with the superheated (1000F) steamat 700 psig from heater coil 12a in line 12 at 14. The thus formedreaction mixture is passed to the initial reaction zone along line 15.The initial reaction zone comprises a suitable vessel 16 of any desiredshape and suitable material and containing a bed 16a of reformingcatalyst.

The reforming reaction in reactor 16 and all other reactors shown isendothermic and accordingly the initial reaction Zone effluent,containing the reaction mixture and carbon oxides and hydrogen in somefinite amount depending on specific reaction conditions, is passed fromthe reactor 16 along line 117 at a reduced temperature, e.g. 920F, and asomewhat lowered pressure owing to the pressure drop across the catalystbed 16a.

The initial reactor to effluent in line 17 is passed through the furnaceconvection section 3 in vheater coil 18 which raises the effluenttemperature to about 1 lOOF for feeding to the intermediate reactors. Inthe illustrated embodiment, the intermediate reactors comprise aplurality of reactors, two beingshown, i.e. reactors l9 and 20 havingcatalyst bedsv 19a and 20a respectively. As will be noted from thebroken lines in the drawing, the number of intermediate reactors may bevaried to provide as many successive reaction stages as desired orrequired to achieve the substantially complete exhaustion ofhydrocarbon, e.g. less than 8 mol percent methane for ammonia synthesisgas and less than 2 mol percent methane for other synthesis, e.g.hydrogen, methanol and Oxo products. Typically between three and eightseparate reactors will be used in an ammonia synthesis gas reformerapparatus accord ing to the present invention. A separate heating coilis provided in advance of each reactor. Thus heater coil 18 precedesreactor 19 and heater coil 2! follows reac tor l9 and precedes reactor24). It will be noted that the several reactors l92 as well as initialreactor 16 and final reactor 22 containing catalyst bed 22a are arrangedfor series flow connection through heater coils 18, 21 and 23 with whichthey alternate and that the successive heater coils progressivelyapproach the radiant heating firebox section 2 of the furnace 1 whereburners 4 are located, i.e. they advance closer to the common heatsource defined by the furnace radiant heat firebox section. Accordingly,the several heater coils impart progressively higher temperatures to thefluids passing therethrough as the successive heater coils move downwardin location within the furnace 1. Typical temperature rises through theheater coils are from 920 to 1100F through heater coil 18 and from 1490Fto 1600F through heater coil 23 leading from intermediate reactor 26 tofinal reactor 22 whence the synthesis gas emerges in line 24 attypically 700 psig and 1530F.

Where an ammonia synthesis gas is to be produced, the effluent fromfurnacein line 24 is passed from primary reactors or reformers I15, 19,2th and 22 to a secondary reactor, or secondary reformer 25, containingcatalyst bed 25a. There nitrogen is added typically in the form ofcompressed air from line 26. The mixed gases from reactor 25 afterprocessing to remove CO and contaminants comprise essentially hydrogenand nitrogen which is passed along line 27 to an ammonia synthesis.

The combustion turbine used to supply preheated oxygen to the furnace 1has mechanical energy output resulting from the combustion and expansionof a compressed fuel-air mixture entering the expander portion of theturbine from line 28. The fuel-air mixture is made and burned at 29 withcompressed air from line 30 and fuel from line3l.

The output shaft of turbine expander 5 is directly coupled tocompressors 32 and 33, compressor 32 operating to compress air fedthereto along line 34 for mixture with fuel at 29 and compressor 33operating to compress air fed thereto along line 35 for use in thesecondary reactor 25. Compressed air from compressor 33 is passed alongline 36, preheated in coil 37 and passed along line 26 into secondaryreformer 25. The flue gas, after preheating secondary air in coil 37 offurnace 1, will be cooled to a temperature where its small remainingheat content allows it to be rejected to the atmosphere. Alternately theresidual heat can be recovered by economizers such as for boiler feedwater preheating, e.g. feed water in line 9 is passed through coil 10 inthe upper end of furnace 1, thereafter venting the flue gas to theatmosphere through stack 8 at an economic temperature, e.g. 400500F.

The compressor 33 thus serves the need of generating compressed gas suchas compressed air in the overall process, making unnecessary thegeneration of great amounts of steam for this purpose in the convectionsection 3 of the furnace 1, which has been the previous practice. Withthe need for superheated motive steam reduced, the furnace duty which isin excess of that required for carrying out the essential reformingreactions and which is to be reclaimed by nonessential auxiliaryconsumers for maximizing the economy of operation, is lowered by from 75to'90 percent. Thus whereas an auxiliary heating duty about equal to thereforming duty has been commonplace in reformer furnaces, i.e. overallheating duty equals 200 percent of reforming heating duty, in thepresent apparatus, the total heating duty is only 1 10-125 percent ofthe reforming heating duty, i.e. only l025 percent above the heatingnecessary to effect the reforming reaction. A savings in heat and thusfuel remains, also, after the fuel consumption of the combustion turbineis taken into consideration.

The advantage of using a combustion turbine (Case B) over steam driverturbines (Case A) for secondary air compression in an ammonia synthesisgas generation with the furnace shown in the FIGURE will be apparentfrom the following table,

The fuel saving is apparent.

Since the heater coils in the reformer furnace no longer containcatalyst they are freed from the restrictions of having to serve as aheated container for solids and flowing gases under pressure. They maynow be made in any diameter or configuration desired. One preferred formof furnace heating element, for example, would be a number of parallelvertical hairpins comprised of tubes of the commonly-used type 304,24-20 Cr-Ni stainless steel, or similar alloy, in the heating zone ofthe furnace and attached to headers of the same or similar material,said headers being insulated from or placed outside of the heating zoneof the furnace to reduce their metal temperature. For example, 2 inch ODtubing (25-20 Cr-Ni) with A inch wall will have adequate structuralintegrity to meet the extreme temperature and internal pressurerequirements in the heating zone of the reforming unit shown. Other tubeforms, sizes, assemblies and materials may, of course, be used in theheating elements without altering the concept of the invention.

The separation of the reactor catalyst mass and of the heat-transferelements into'a plurality of discrete units gives unusual flexibility tothe reformer. First, it allows TABLE COMPARISON OF DUTIES (For 1000Short Tons/Day Ammonia Using Naphtha Feed and Fuel) CASE Type of DriveTurbines: A B

l. Secondary Air Compressor (l0,l30 BHP) Steam Combustion 2. Other majorpumps and Compressors Steam Steam Naphtha Consumption lbs/hr):

1. Feed 43,685 43,685 2. Fuel 26,375 21,975 3. Total 70,060 65,660

Reformer Furnace Dutues (l0 Btu/hr).

1. Primary Reforming A. In radiant section 245.0 l74. B. In convectionsection 0 71. C. Total 245.0 245.

2. Process Steam Superheating 24 24 3. Secondary Air Preheating l9 l9 4.Total Reforming Reaction 288 288 5. To Auxiliary Consumers 253 72 6.TOTAL Furnace Duty 54l 360 Steam Quantities (lbs/hr):

1. High Pressure Steam Generated 452,000 366,000 2. Exhaust SteamCondensed 196,000 124,000

Total Plant Cooling Water gal/min 39,300 32,000

greater freedom in varying the catalyst formulation as regards bothparticle size and shape, and chemical composition. For example, in thereforming of light hydrocarbons such as naphtha, as typified by equation(2), his postulated that the first action is pyrolysis or hydrocrackingof the naphtha, followed by chemical reaction with steam. The lastsurvivor of the cracking of the feedstock is held to be the mostrefractory hydrocarbon, methane. The catalyst employed in the initialreactor (to which is sent the preheated steamhydrocarbon feed mixture)can be a catalyst tailored for effectively rupturing carbon-to-carbonbonds without laying down deposits of troublesome coke or carbon.Catalyst used in subsequent beds can be specifically formulated to aidthe reforming reaction. Catalyst composition may also be graduated, ifdesired, to match the change in composition of the process gas as itflows from stage to stage in the process. The benefits from so varyingthe catalyst formulation from stage to stage include maximizing theactivity and life of the catalysts (thus lowering their initialinstallation and re placement costs) as well as improved processperformance by more nearly attaining equilibrium gas composition (lowermethane leak) at a given gas outlet temperature relative to a catalystwhose composition is a compromise for the average gas composition in theconventional reformer tubes.

Secondly, the flexibility in the utilization of heat in the presentprocess reforming furnace leads to the possibility of significant fuelsavings and further reduction in furnace costs. In the conventionalreformer, the reforming reaction cannot be conveniently carried outother than entirely in the radiant section of the furnace.

As noted before, the entire conventional reformer tube sees the burnerflames and the products of combustion leave the radiant section attemperatures above 1900F after supplying the heat required to performthe reforming reaction. Cooling these flue gases to 500F or less for thesake of economical heat utilization before venting them to theatmosphere will result in the availability of a quantity of heat ofabout the same magnitude as that used to conduct the reforming reaction.The minimum fired duty for the conventional reformer furnace is thenabout double that required to satisfy the reforming reaction. Economy ofoperation thus requires that means must be found for utilizationelsewhere in the process or plant of at least one-half of the fired dutyof this conventional reformer furnace.

In the scheme depicted in the FIGURE, however, it is possible to locatethe lower temperature reheat coils, e.g. coil 18, in the convectionsection 3 of the furnace 1 rather than placing all the'reheat coils inthe radiantly heated furnace section 2. A closer approach to truecounter-currency may then be achieved between the combustion gases andthe vapors being reformed. The minimum fuel consumption of the furnaceis no longer dictated by the total heat requirements of the reformingreaction supplied as radiant heat and can be considerably less than forthe conventional reforming furnace.

I claim:

1. Apparatus for generating a synthesis gas from a hydrocarbon feedcomprising A. plural primary adiabatic reactors including an initialprimary reactor, at least one intermediate primary reactor and a finalprimary reactor in series flow connection, B. means heating thehydrocarbon feed to the reactors including bl. a longitudinally extendedfurnace having a firebox at one end defining a higher temperatureradiant heating section, and a lower temperature convection heatingsection beyond the firebox, said reactors being located outside thefurnace, and

b2 plural heaters flow connected withsaid reactors in alternatingrelation including a first heater in the convection heating section ofthe furnace for said initial primary reactor, a second heater for theintermediate primary reactor in the convection heating section of thefurnace between the radiant heating section of the furnace and saidfirst heater and a heater in the radiant heating section of the furnacefor the final primary reactor arranged to pass the hydrocarbon feedprogressively from the lower temperature convection heating section tothe higher temperature radiant heating section of the furnace and insequence alternately through said heaters within the furnace and theirreactors outside the furnace to produce a primary reactor effluent;

C. secondary reactor means comprising a secondary reactor in whichcompressed air is reacted with the primary reactor effluent;

D. combustion turbine means arranged to exhaust oxygen-containingcombustion gases into said furnace for combustion with fuel.

E. a centrifugal air compressor coupled to the output shaft of thecombustion turbine means arranged to supply compressed air to thesecondary reactor, and

F. air heating means within the convection section of the furnace toheat the compressed air being passed to the secondary reactor.

=i= l= =l

